by
David Mitzi, Teodor K. Todorov, Jiang Tang, Santanu Bag, Oki Gunawan, Tayfun
Gokmen, Yu Zhu, David B. Mitzi
Energy from the sun reaching the earth’s surface amounts to
several thousand times our global consumption of electricity. Yet electricity
from photovoltaic (PV) solar cells currently contributes significantly less
than one percent of worldwide production. Of the numerous existing PV
technologies, none so far have combined the virtues of being highly efficient,
cheaply scalable and made with abundantly available materials.
IBM’s Materials Science team has partnered with Solar
Frontier, Tokyo Ohka Kogyo (TOK) and DelSolar to develop an efficient and
affordable PV cell made of abundant natural materials. So far, the tests of our
Cu2ZnSn(S,Se)4 (made of readily available copper, zinc,
and tin, and referred to as CZTS) thin-film devices have achieved a
world-record PV solar-to-electric power conversion efficiency of 11.1 percent
(10 percent better than any previous reports) for this class of semiconductors.
And it can be manufactured by simple ink-based techniques such as printing or
casting.
What makes CZTS
better
Currently, the most widespread PV semiconductors, made of
crystalline silicon, are abundant and highly efficient. They’re in panels used
for everything from home electricity to the International Space Station.
However, they have extremely high material purity requirements (>99.9999
percent!), and the wafers are typically cut from large solid ingots and wired in
series to form PV modules – making it expensive and difficult to upscale.
Photos of IBM's CZTS Solar Cell Device.
Other thin-film chalcogenide materials
used in PV cells, such as Cu(In,Ga)(SSe)2 (CIGS) and CdTe, have been
developed to a performance level close to that of silicon, with inherently more
scalable processing. They are directly deposited on large-area, low-cost
substrates such as glass, metal or plastic foil. While CIGS and CdTe are easy
to integrate into buildings and consumer products, their compounds contain rare
and expensive elements that increase cost and limit their manufacturing levels
to less than 100 Gigawatts per year (worldwide continuous electricity
consumption is 15 Terawatts – 150 times greater than the level of what these
CIGS can produce).
Our CZTS PV cells could potentially yield up to 500 GW/year
– getting closer to the Terawatt levels of renewable electricity the planet
needs.
The focus of our joint-development team remains to further
increase this device efficiency and transfer the technology to
environmentally-friendly, high-throughput industrial manufacturing. The hope is
that within several years this new class of photovoltaic materials will begin
to contribute to the wider availability of lower-cost solar electricity.